NEUEOPTERA— ODONATA. 125 



most abundant, the Aeschnida; being represented by a species of Aeschna 

 at Schambelen and the Gomphidse by one species each of Petalura 

 and Goinphoides from Enghxnd. Calopterygidfe come next, with one 

 species each of Tarsophlebia and Heterophlebia, both extinct genera, also 

 from Enghmd, and finally a species of Libellula from England. The same 

 relation Iiolds in passing upward into the oolite, where the Agrionina are 

 added. Here we have thirty-two species, of which half are Agrionina: four 

 Agrionidfe, and twelve Calopterygidas of five genera, mostly extinct, namely, 

 Isopldebia, two ; Heterophlebia, two ; Stenophlebia, three ; Tarsophlebia, 

 one, and Euphjea, four; three are Aeschnidje of the genera Anax and 

 Aeschna ; eight Gomphidaj of some undetermined genera, besides Petalura 

 and Petalia; and finally five Libellulida^ of about as many genera, yet 

 undescribed. A species of Gomphidse has also been found in the Wealden 

 of England. Tlie lithographic slates of Bavaria afi'ord numerous, some- 

 times wonderfully preserved, dragon-flies, called by the workmen Stangen- 

 reiter or Schladen-Vogel, which have been carefully studied by Hagen. 

 They lie on the stone with expanded wings and are generally larger than 

 modern types ; sometimes the most delicate veins are perfectly preserved. 

 Most of them are referred to extinct genera. 



Considering the comparative abundance of this group in the Second- 

 ary rocks one would expect to find a better representation in the Terti- 

 aries than is the case, for, even counting all the species founded upon the 

 immature stages as distinct from any of those established upon wings, the 

 Tertiary species are less than twice as numerous as those from the Second- 

 ary rocks. The subfamilies are about equally represented, though the 

 Agrionina are a little in excess, and the species are very unequally distrib- 

 uted among the tril)es. Thus there are twentv-two species of Agrionidaa of 

 the following genera : Agrion, seven; Lestes, five ; Argya, one; PJatycne- 

 niis, two; Sterope, one ; Dysagrion, three ; Podagrion, one ; and Lithagrion, 

 two, the last four genera being extinct ; wliile there is but a single species 

 of Calo))terygida?, known by a pupal form, from amber, a curious reversal 

 of the pi'oportion in Mesozoic rocks. The ^Eschnina are more equally 

 balanced between the tril)es, the Gompliidaj being represented l)y six 

 species, of the genera Gomphus, Gomphoides, Ictinus, and Petalura, and 

 the Aeschnidfe by nine ; of the genera Aeschna (eight) and Anax (one). 

 The Libellulina, however, have again only a single species of CorduHd;e, 



